Conventionally, scroll compressors have been widely known which are used for, e.g., refrigeration systems, etc., to compress fluid, such as refrigerant.
Japanese Patent Publication No. 9-170574 describes a scroll compressor of this type. This scroll compressor includes a compression mechanism having a so-called asymmetric scroll structure. For this compression mechanism, a fluid compression chamber is formed by allowing a fixed scroll wrap to mesh with an orbiting scroll wrap. The compression chamber is sectioned into a first compression chamber facing the outer peripheral surface of the orbiting scroll wrap and a second compression chamber facing the inner peripheral surface of the orbiting scroll wrap. Furthermore, a suction port for leading fluid to the compression chambers is formed near the outer peripheral surface of the compression mechanism. A discharge port for discharging fluid compressed in the compression chambers to the outside (discharge space) is formed in the middle of the compression mechanism. For this scroll compression mechanism, an orbiting scroll eccentrically rotates relative to a fixed scroll. Consequently, each compression chamber gradually moves inwardly from the vicinity of the outer periphery of the compression mechanism so that its volume decreases, resulting in fluid compressed in the compression chamber.
Here, the volume ratio (compression ratio) of such a scroll compressor is set at a predetermined constant value to meet rated operating conditions of a refrigeration system, etc. Therefore, for example, under operating conditions where the pressure differential between high and low pressure regions of a refrigeration system is relatively small, a phenomenon in which refrigerant is excessively compressed by a compression mechanism, i.e., so-called over-compression, occurs. This significantly reduces compression efficiency.
To address the above-mentioned problem, in the scroll compressor of Japanese Patent Publication No. 9-170574, the compression mechanism is provided with relief ports in order to avoid such over-compression. More specifically, in the compression mechanism, an end plate for a fixed scroll is provided with six relief ports (bypass ports). Three of these relief ports correspond to the first compression chamber, and the other three relief ports correspond to the second compression chamber. Each relief port is provided with an openable and closable relief valve. For this compression mechanism, for example, under operating conditions where the pressure differential between the high and low pressure regions is small, the relief port is opened. As a result, refrigerant that is being compressed in each compression chamber is delivered through the associated relief ports to the outside (high-pressure space), thereby avoiding the above-described over-compression.